1. Field of the Invention
The invention relates to an aircraft engine control system. In particular, the invention concerns an emergency engine control system which will be found especially useful in single engine installations.
2. Description of the Prior Art
The invention is particularly concerned with control of jet engines. The normal engine control system utilises a system of monitoring engine performance and generating necessary control inputs to maintain certain engine parameters within predetermined limits. The main areas of control are shaft speeds and exhaust gas temperature. The most recent types of control system employing microprocessors and the like evaluate sophisticated steady state and transient control functions and are able to exercise control over a greater number of operating variables within the engine. Basically, should any of the monitored variables approach the limits of safe operation fuel flow is reduced to maintain shaft speed or gas temperature at a safe level.
Over and above this level of safe control there is normally provided a separate overspeed governor which is independent in its operation. Its sole purpose is to prevent the engine exceeding a maximum safe speed. Thus, in the event of control system malfunction the governor may be relied on to preserve engine integrity. Consequently the control system can be designed with a fail-safe mode which allows fuel supply level, and therefore engine speed, to increase. It is considered preferable for aircraft safety to permit engine thrust to increase in the event of control system failure rather than shutting down the engine. Although multi-engined aircraft can be flown safely with one engine stopped it is not generally a viable option for a signal-engined aircraft.